Tuning emission color of Eu2+-activated phosphor through phase segregation

Abstract

Different applications have diverse requirements on the luminescence performance of the phosphors. Therefore, tuning emission spectrum of phosphors is a perpetual topic. In this work, we utilize phase segregation to effectively adjust the emission spectrum of a Eu2+-activated phosphor system. The introduction of Ba2+ ions into K2Ca(PO4)F:Eu2+ (simplified as Ba-KCP:Eu2+) facilitates the emission spectral tuning, which results in the variation of emission color from red to cyan. Crystal structural and phase analyses indicate that the spectral tuning results from the gradual segregation of a second phase K2BaCa(PO4)2 and the transfer of Eu2+ from K2Ca(PO4)F to K2BaCa(PO4)2 phase upon increasing Ba2+ content. Phase segregation within a phosphor particle is beneficial to ensure the stability of devices’ performance when it is used to fabricate phosphor-converted light-emitting diodes (pc-LEDs). The composite phosphor Ba0.06-KCP:0.005Eu2+ exhibits white light emission with appropriate cyan and red-emitting component. The internal and external quantum efficiencies (QE) of the white-emitting Ba0.06-KCP:0.005Eu2+ phosphor are 90 and 54 %, respectively, close to other Ba-KCP:0.005Eu2+ samples. The PL intensity of the white-emitting Ba0.06-KCP:0.005Eu2+ at 150 °C is 89 % of that at room temperature. The luminous efficacy of the pc-LEDs based on 365 nm chip and the Ba-KCP:0.005Eu2+ phosphor can be as high as 73.9 lm/W. The performance of Ba-KCP:0.005Eu2+ based on phase segregation is superior to that based on the variation of crystallographic site for Eu2+ within K2Ca(PO4)F phase. The high QE values, excellent thermal stability, and the performance on pc-LEDs exhibit the potential application for the phosphors in plant growth and solid-state lighting.